This section provides background information related to the present disclosure, which is not necessarily prior art.
When the temperature is cold, it is desirable to heat the passenger cabin of a vehicle as quickly as possible to improve passenger comfort. Current vehicle heating, ventilation, and air conditioning (HVAC) systems draw airflow from the outside environment surrounding the vehicle into the HVAC system and heat the airflow using heat generated by the engine. The airflow is then introduced into the passenger cabin to heat the passenger cabin.
While current HVAC systems are suitable for their intended use, they are subject to improvement. For example, heating cold external airflow requires more than an insignificant period of time, which results in the occupants having to endure a cold passenger cabin until the engine reaches a temperature that is warm enough to expeditiously heat the external airflow. HVAC systems that recirculate the relatively warmer airflow of the passenger cabin through the HVAC system in place of the external airflow in order to expedite heating of the passenger cabin have been contemplated, but have failed because the cabin air has a relatively high humidity that causes the windshield and windows of the vehicle to fog. The present disclosure advantageously provides for an improved HVAC system that addresses these shortcomings of the art, and thus is able to heat recirculated passenger cabin airflow during a cold engine start to improve passenger cabin warmup time without fogging the windshield or windows of the passenger cabin. The present disclosure provides numerous additional advantages and unexpected results as explained in detail herein, and as one skilled in the art will appreciate.